Simplify workspace creation with inline worktree API

Replace the multi-step new-agent route flow with a single
create_paseo_worktree endpoint that registers the workspace immediately
and creates the git worktree in the background. The sidebar now calls
this endpoint directly and shows a creating spinner inline.

Also auto-resolves the base branch from origin/HEAD when not explicitly
provided, removes the unused Tauri WebSocket transport layer, and
normalizes loopback endpoints to localhost.

Closes #125

packages/server/src/utils/checkout-git.ts

@@ -708,7 +708,7 @@ async function hasOriginRemote(cwd: string): Promise<boolean> {
   return url !== null;
 }
 
-async function resolveBaseRef(repoRoot: string): Promise<string | null> {
+export async function resolveRepositoryDefaultBranch(repoRoot: string): Promise<string | null> {
   try {
     const { stdout } = await execAsync("git symbolic-ref --quiet refs/remotes/origin/HEAD", {
       cwd: repoRoot,
@@ -755,6 +755,10 @@ async function resolveBaseRef(repoRoot: string): Promise<string | null> {
   return null;
 }
 
+async function resolveBaseRef(repoRoot: string): Promise<string | null> {
+  return resolveRepositoryDefaultBranch(repoRoot);
+}
+
 function normalizeLocalBranchRefName(input: string): string {
   return input.startsWith("origin/") ? input.slice("origin/".length) : input;
 }